1. Field of the Invention
This invention relates to improvements in electronic circuits, and more particularly to improvements in linear and logarithmic signal conversion circuits, and to improvements in linear and logarithmic voltage and current conversion circuits in which the improved cascode mirror circuits may be embodied.
2. Relevant Art
In the past, circuits used for signal conversion, more particularly voltage-to-current or current-to-voltage conversion, suffered numerous deficiencies. Often, for example, the linearity of the circuits was affected by parasitic emitter or base resistors of the transistors used in their design. Additionally, since typically the input to most widely used circuits is applied to the base element of an input transistor, a high swing capability could not be achieved.
Most of the circuits previously employed used operational amplifiers or buffers in closed loop structures, as well as PNP-type transistors, and, consequently, the speed of the circuit was less than that which might otherwise have been achieved. In order to make closed loop systems stable, compensation capacitors were typically employed. Such compensation capacitors, however, resulted in lower speed and overall larger sized circuits. The necessary PNP transistors of many circuits made their stability even more difficult to ensure.
Furthermore, many of the circuits previously employed produced an output that was dependent upon the beta of the transistors of the circuit. This resulted in a loss of high temperature stability of their transfer function.